One-Minute Physics: How wind can take down a bridge

In physics textbooks, the dramatic collapse of the Tacoma Narrows Bridge in 1940 is often attributed to resonance. But in this animation, producer Henry Reich explains how a destructive, self-feeding vibration is actually responsible for the disaster. The same phenomenon can also cause airplane wings to shake so vigorously that they disintegrate or it can make swings appear to move on their own in a ghostly fashion. A variation of the effect could also be harnessed to generate energy.

...leads to greater aerodynamic forces in a feedback process. These interactions may become smaller until a condition of equilibrium is reached, or may diverge catastrophically if resonance occurs.

Maybe you could tone down "the whole world has it wrong" attitude.

paul black
on December 14, 2011 5:45 PM

The slightly smug tone is let down by repeating the hoary old myth that a sung note can shatter a wine glass. If this could actually happen no watch-glass, binoculars or spectacles would be safe in an opera house and police forces the world over would have recruited sopranos into riot control.

Alan
on December 14, 2011 7:59 PM

JON
Wikipedia is a source of information put forward by the people. Not always with references and hence somje of the iformation may be suspect. Remember the old saying "Consider the source".

Paul
Did you not see that episode of Mythbusters?
They gota guy to sing a note and break a wineglass.
A lot of it was down to how long he could hold the note for, how much oomph he put behind it and the response of the individual glass but it did happen. That's not to say it will happen regularly, but it did Happen.

Cletis
on December 14, 2011 8:29 PM

Reich states unequivocally that the cause of the collapse was not resonance. Then he makes the case that it was resonance; but that the cause of the resonance was aeroelastic flutter instead of well-timed gusts of wind. Apparently, he does not know that flutter can result in destructive resonance, and that the bridge would not have collapsed if the flutter had not found a destructive resonance -- just as it would not have collapsed if gusts of wind had failed to produce a sufficient resonance in the theory he is arguing against.

Most people don't say the failure was SIMPLY due to resonance. Most people say that resonance led to a larger-than expected twisting motion; the large twist then "valved" a wind force acting on the bottom of the bridge, which formed a positive feedback loop with the resonance. Finally the motion was too large for the bridge to take.

Not clear who the author is trying to debunk or correct, because I haven't heard a simple resonance explanation in several decades!